Skulls

While visiting my parents in Idaho this Christmas, I went down a canyon with my dad. I've been taking a greater interest in bones lately so I gathered a bunch of them when I found a big set of owl pellets and a few bones along the edge of the canyon. My dad also found a nice skull under a bush while fishing along the creek.

Now that I'm back home and have access to my copy of Elbroch's Skulls book I've been looking over the skulls and figuring out what they are from. So far I believe I figured out the two here to genus at least, and know that there are at least two other species in the collection.

There are a lot of details visible in these pictures that can be used to figure out who the skull belonged to, but it would be difficult to go through very many of them. Instead, I will just go over a few of the main details I used. For reference the first skull in each pair is about 6.5 cm and the second skull is about 5 cm. Both are clearly rodents from the teeth, so I'll go from there.




The first skull ended up being pretty easy for me to identify because of its size and the way the brain case sticks out squarely over the eye socket. Just flipping through the pictures of skulls I saw that it matched up with the muskrat (Ondatra zibethicus).

The second skull has a well developed post orbital process (the sharp protrusion over the eye socket). As far as I can tell, among rodents, those seem to mainly occur in the squirrel family.




At first I thought the second skull might be a type of marmot because of the shape of the post orbital process (and because they are large members of the squirrel family). However when going through the details of the marmots things kept not seeming to match up quite right. What finally convinced me that it wasn't a marmot was that marmot skulls are pretty flat on top, somewhat similar to the muskrat skull, however this skull is fairly rounded. In hind sight the skull was smaller than the range given for marmots as well. With a little more searching, I found that ground squirrels (Spermophilus sps) fit the skull much better.

A couple of differences to note are the position of the zygomatic arch (the bone that forms the outer portion of the eye socket) and how curved (or straight) the incisors are. I don't know that these are more useful details to pay attention to than others, but they seem fairly easy to pay attention to.




A couple of differences I notice on the ventral view are the size and shape of the palate, the relative position of the teeth (including parallel vs. angled) and the size and position of the incisive foramina (the narrow pair of holes behind the incisors).

I have not yet got down to species on the ground squirrel. There are a couple of different ground squirrel species in that region of Idaho that aren't in the skulls book and the skull doesn't seem to match up exactly with the ones that are.

Trailing Bobbie

It snowed a bit at the beginning of the month here. It worked out nicely for the first day of the tracking intensive weekend, though not so well for the second day as it had snowed all that night so covering up all the tracks. Then it started to rain and flooded the valley a bit, but that is for another post perhaps.

We went back on the logging roads behind the school's land with the intention of doing some sign tracking. My subgroup decided to head down toward the creek and check out aplodontia sign along the way. There certainly was plenty of that, and while exploring the holes and tunnels we came upon the trail of a bobcat. It's hard to turn down the chance to follow a fresh bobcat trail even if we were supposed to be sign tracking, so off we went. (And hey - we could look for bobcat sign along the trail!)



It's interesting to see how much a bobcat can splay its foot. The above picture shows that this is a relatively small bobcat, but when it walked out on some ice (and apparently decided that perhaps the ice wasn't as solid as it would like) its track splayed out to almost twice the width.



Before we even found these bobcat tracks, one of the goals for the day was to find some bobcat scent marking. So we were keeping our eyes out for that sort of thing. Whenever we found the tracks stop we would look (and smell) around to see if it had marked there. Not too long after we started on the trail there was a place where it had stopped, we smelled around and some in the group decided that a section of a nearby tree smelled of "asparagus pee", but it did not seem connected to the bobcat. However just 10 feet away there was another quick stop where the cat had turned its butt towards a dead fern. Jackpot. It smelled strongly of cat piss.



I've been told that animals like to scent mark things that will hold the smell for a long time. Punky wood was given as a good example because the smell will be able to soak in. So I'm curious about using the fern, perhaps the dead vegetation will hold the smell well until it completely decays, so would be good for a season or two. As far as I can tell, this was done primarily for marking rather than to empty the bladder as I didn't see any particular yellow marking or dripping on the snow around the fern.

Apparently both males and females can spray urine behind them - I'm not really sure how that works - so the marking doesn't really help me out with gender id. However given the size I would think it was either a female or a young male. There are track features that can be used to determine sex and hopefully I will be able to use those at some point, but at the moment I'm not very knowledgeable about using those.

A Delicacy

Last week I found a large salmon carcass along the river. There have been a lot of chum salmon carcasses along the river in previous weeks (with mainly just bones remaining now), but I think this was a king salmon and the only one I've seen on the river so far. My impression is that their population is much smaller than dog or pink salmon in the area, which may be the reason I have not seen any before now. I also wonder though if they prefer to spawn further up river and so aren't as likely to be found dead down here.

I don't know what the cause of death was, but I have to wonder if it was one of the many fishermen I have seen along the river. I don't get the impression that the salmon are legal to keep, perhaps it became injured while being caught and released and died subsequently. I've only talked with a few of the fishermen I've seen down there, but all the ones I have talked to seemed unwilling or unable to say what they were fishing for. My impression was that they were pretty novice and were just out to fish without worrying much about what they might or might not catch.



The next morning the carcass was already picked pretty clean. I was a bit surprised since most of the salmon carcasses I see mostly just get pecked at (eyes and brains seem to be favorites). I guess this one tasted a bit better as it was a lot fresher than the spawned out salmon that otherwise had washed up.